During normal use, contact lenses become soiled or contaminated with a wide variety of compounds that can degrade lens performance. For example, a contact lens will become soiled with biological materials such as proteins or lipids that are present in the tear fluid and which adhere to the lens surface. Also, by handling of the contact lens, sebum (skin oil) or cosmetics or other materials can soil the contact lens. These biological and external contaminants can affect visual acuity and patient comfort. Accordingly, it is important to remove any debris from the lens surface for continued comfortable use with a lens care solution that contains one or more cleaning components.
Ophthalmic compositions formulated as a lens care solution must also contain one or more disinfectant components. Presently, the two most popular disinfectant components are poly(hexamethylene biguanide), at times referred to as PHMB or PAPB, and polyquaternium-1.
As stated, PHMB is presently used in contact, lens care solutions. These PHMB-based care solutions represent a significant improvement in patient comfort and antimicrobial effectiveness compared to most other antimicrobial components. However, as with any antimicrobial component there remains a tradeoff between the concentration of the antimicrobial component in the solution and the comfort experienced by the patient. Due to its wide commercial acceptance, extensive efforts have been directed to improve the antimicrobial efficacy or the comfort level to the patient by chemically modifying PHMB.
Another approach is to use two antimicrobial components, each at lower concentrations than if the two antimicrobial agents were to be used individually. The goal being that the two antimicrobial components would exhibit some form of a synergistic biocidal affect.
U.S. Pat. No. 5,840,671 describes a contact lens solution that contains a tertiary amine oxide and an anionic surfactant in the form of a triethanolamine salt. These two cleaning components are present in the solution at a total concentration from 0.1 wt. % to 20 wt. %. Also the weight ratio of the tertiary amine oxide to the anionic surfactant is from 1:4 to 30:1. It is said that the combination of the tertiary amine oxide with the anionic surfactant provide a “higher degree of cleaning effect than any cleaning solution which employs only one of those two kinds of surface active agents.” Also, if the total amount of tertiary amine oxide and anionic surfactant is less than 0.1 wt. %, the lens solution “does not exhibit a satisfactory cleaning effect”.